Physics
Assertion (A): The bottoms of cooking utensils should be kept smooth and shiny.
Reason (R): Smooth and shiny surfaces are good reflectors of heat.
- Both A and R are true and R is the correct explanation of A
- Both A and R are true and R is not the correct explanation of A
- A is true but R is false
- A is false but R is true
Answer
A is false but R is true
Explanation
Assertion (A) is false because the bottoms of cooking utensils should not be smooth and shiny; instead, they are usually made dull or blackened to absorb heat more effectively.
Reason (R) is true because smooth and shiny surfaces are good reflectors of heat and poor absorbers.
Therefore, A is false but R is true.
Related Questions
The vacuum kept in between the walls of a thermos flask reduces the heat transfer by:
- conduction only
- convection only
- radiation only
- conduction and convection
Assertion (A): A reading of 32 °F on a thermometer equals 0 °C.
Reason (R): The Celsius scale is commonly used in most countries for measuring temperature.
- Both A and R are true and R is the correct explanation of A
- Both A and R are true and R is not the correct explanation of A
- A is true but R is false
- A is false but R is true
Fill in the blanks:
(a) Heat is a form of …………… .
(b) …………… determines the degree of hotness or coldness of a body.
(c) On heating a body, its temperature …………… .
(d) We use a …………… for measuring the temperature of a body.
(e) The S.I. unit of temperature is …………… .
(f) In a thermometer, the commonly used liquid is …………… .
(g) The temperature of a normal human body is …………… °C.
(h) A person is said to have fever if his body temperature is more than …………… °F.
(i) A hot metallic piece is placed in tap water contained in a bucket. Heat will flow from …………… to …………… .
(j) The temperature of boiling water is …………… .
(k) Liquids expand …………… than solids.
(l) Gases expand …………… than liquids.
(m) Heat transfer in solids is by …………… .
(n) Heat transfer in liquids and gases is by …………… .
(o) Metals are …………… of heat.
(p) Still air is an …………… of heat.
(q) Black and dull surfaces are …………… of heat.
Write true or false for each statement:
(a) On touching a lump of ice, we feel cold because some heat passes from our body to the ice.
(b) Heat flows from a body at a high temperature to a body at a low temperature when they are kept in contact.
(c) All solids expand by the same amount when heated to the same rise in temperature.
(d) Telephone wires are kept tight between two poles in summer.
(e) Equal volumes of different liquids expand by different amounts when they are heated to the same rise in temperature.
(f) Solids expand the least and gases expand the most on being heated.
(g) A mercury thermometer makes use of the property of expansion of liquids on heating.
(h) Kerosene contracts on heating.
(i) Water is a bad conductor of heat.
(j) Medium is necessary for the transfer of heat by radiation.
(k) Land and sea breezes are convection currents of cold and warm air.
(l) Liquids are heated by conduction and radiation.
(m) Black surfaces are poor absorbers of heat radiations.